Recently, with the development of personal computers, in particular, with the development of portable personal computers, a demand for a liquid crystal display, particularly for a color liquid crystal display has been increased. However, since the color liquid crystal display is expensive, there is an increasing demand for cost reduction. In particular, cost reduction for a color filter, whose proportion in the cost is high, is highly requested.
Such a color filter is normally provided with coloring patterns of three primary colors of red (R), green (G) and blue (B). A liquid crystal can be operated as a shutter by powering on and off electrodes respectively corresponding to each of pixels of R, G and B, and light passes through the each pixel of R, G or B so as to display color images.
Detail portions of the color filter such as the pixel part, a pillar-like spacer, a protect layer or the like can be provided by forming a coating layer of a predetermined pattern using a resin, drying and solidifying the same, and as needed, further curing the same by the cross-linking reaction.
To the resin layer comprising the details, a performance to a certain degree is required in terms of the common physical properties as a layer such as the adhesion property, the evenness of the layer thickness, the strength, the hardness and the heat resistance which does not cause thermal shrinkage or decrease of the layer thickness in the color filter production process. Moreover, for example, to the resin layer as the pixel part whose optical characteristics are regarded as important, it is required to have the excellent characteristics particularly in terms of the pattern shape accuracy, the transparency, and the discoloration resistance or the like.
Further, in the present circumstances that a liquid crystal display device is required to display more high-quality and precise images, reduction in resistance and thickness of ITO (Indium Tin Oxide) transparent electrode is necessary as a solution. Accordingly, sputtering at higher temperature is required to be included in the ITO transparent electrode forming process. Thus, a resin layer making up detail portions of a color filter is also required to be heat resistant in the formation of the ITO transparent electrode at such high temperature.
As a conventional method of producing a color filter, for example, there is known a dying method. According to the dying method, first a layer of a water-soluble polymer material as a dying material is formed on a glass substrate, patterning the same in a desired shape by a photolithography process, and soaking the obtained pattern in a dying bath so as to obtain a colored pattern. By repeating the operation for three times, R, G and B color filter layers can be formed.
As another method, there is a pigment dispersing method. According to the method, first a photosensitive resin layer with a pigment dispersed therein is formed on a substrate. A single color pattern is obtained by patterning the same. By repeating the same operation for three times, color filter layers of R, G and B can be formed.
As still another method, an electro-deposition method, a method of dispersing a pigment in a thermosetting type resin, printing three times for R, G and B, and thermally setting the resin or the like can be presented.
However, the same process should be repeated for three times in either method of coloring the three primary colors of R, G and B, and thus a problem of cost increase and a problem of a decrease in yield due to the repetition of the same process, are involved.
As a production method of a color filter capable of solving the problems, in Patent Document 1, a method of forming a coloring layer (pixel part) by shooting a colored ink containing a thermosetting resin onto the substrate surface by the ink-jet method and heating the same is disclosed.
In order to form the pixels by shooting the ink Patent Document 2 according to an accurate pattern by the ink-jet method, straightness and sustainability are required at the time of the ejecting operation from the ejection head. However, in the case where the evaporation rate of the ink is too high, the ink viscosity is increased drastically at the nozzle end of the ejection head so as to exhibit multiple ejections or deflection of shooting direction of the ink droplets, or clogging is generated in the case of intermittent ejection with a time interval so as to disable the re-ejection.
Moreover, in the case of forming the details of the color filter with a thermosetting type resin, it is common to utilize polymerization and/or the cross-linking reaction of the acid component and the epoxy component. In order to improve the strength, the hardness, the heat-resistance or the like of the cured layer, it is preferable to increase the cross-linking density of the cured layer. In order to increase the cross-linking density of the epoxy-based thermosetting type resin layer, it is preferable to increase the reactive site concentrations of the acid component and the epoxy component in a coating liquid or a coating layer formed from the coating liquid as much as possible. However, since the acid component can hardly be dissolved in an organic solvent, it has been difficult to have a large amount of acid component coexisting in the coating liquid (in the reaction system). Moreover, even in the case where a sufficiently large mount of the acid component corresponding to the epoxy component amount can coexist in the coating liquid, a deterioration in the time passage stability is caused due to too high reactivity of the coating liquid, as a result, the viscosity change (in particular the viscosity rise) can easily be generated in a short time so that there is a risk of difficulty in stable ejection by the ink-jet method.
To solve the problems, Patent Document 2 discloses an ink-jet ink composition for a color filter with the use of a blocked carboxylic acid curing agent. Herein, a curing agent in which aromatic carboxylic acid is blocked is preferably used; however, in the case of using a curing agent containing an aromatic group, storage stability, for which there is an increasing demand in recent years, is not always sufficient.
Patent Document 1: Japanese Patent Application Laid-Open No. Hei. 9-21910
Patent Document 2: Japanese Patent Application Laid-Open No. 2003-66223